1. Field of the Invention
The invention relates to a technology for circuit boards which have an insulating layer containing a fibrous filler. In particular, the invention relates to a technology for circuit boards in which metal or other conductor parts have excellent adhesion to the insulating layer, and the metal or other conductor parts formed on the insulating layer provide an excellent heat radiation capability.
2. Description of the Related Art
With the advances of LSIs in performance and functionality in recent years, their power consumption has also been on the increase. Furthermore, with the miniaturization of electronic equipment, smaller sized substrates have also required, along with higher densities and multilayer structures. The power consumption per unit volume of a circuit board (heat density) has therefore been growing, and measures to address this increased heat radiation have been increasingly demanded.
There is a structure known for multilayer boards in which vias are formed in order to establish conduction between the individual layers of the multilayered boards. This structure is known to suppress rises in temperature. Insulating layers made of a mixture of resin and glass fibers have also been used to provide improved strength and functionality.
Japanese Patent Laid-Open Publication No. Hei 5-55401 discloses a printed wiring board having a spot-faced organic resin substrate, in which a large number of hair-like fibers exposed in the sidewalls of the formed recesses are covered with a through-hole plating layer.
Japanese Patent Laid-Open Publication No. 2002-237681 discloses a printed wiring board having an insulating substrate, in which solder filling holes for preventing solder from coming off the insulating substrate are formed by laser irradiation so that the ends of fibers protruding from the sidewalls bite into the solder.
The fibers exposed perpendicularly from the sidewalls of the recesses, however, can only have lengths as long as coverable by the through-hole plating layer, i.e., their length is dependent on the thickness of the copper plating. For that reason, the copper plating may possibly exfoliate from the insulating resin when exposed to high heat loads.
Moreover, with the multilayer boards, it is not always possible to fill the holes with solder in every location. Furthermore, when the through-hole plating layer just covers the fibers just flatly, it can only provide substantially the same heat radiation capability as that of ordinary plating layers.